THE CONCRETE BRIDGE MAGAZINE

SUMMER 2016

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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C O N C R E T E B R I D G E T E C H N O L O G Y
36 | ASPIRE Summer 2016
commonly used name and definition in the United States is the one introduced by
Graybeal
3
: "UHPC-class materials are cementitious-based composite materials with
discontinuous fiber reinforcement, compressive strengths above 21.7 ksi (150 MPa),
pre-and post-cracking tensile strengths above 0.72 ksi (5 MPa), and enhanced durability
via their discontinuous pore structure." In comparison, conventional concrete is without
fibers and typically has a compressive strength of 4 to 10 ksi.
The ingredients of a UHPC mixture can vary. Early mixtures generally consisted of
about 1200 lb/yd
3
(700 kg/m
3
) of portland cement, 25% silica fume, 25% silica powder,
and fine sand with maximum grain size of 0.03 in. (0.8 mm). A very low water-binder
ratio of 0.16 to 0.20 was used. For flowability, a large quantity of high-range water-
reducing admixture must be used. Steel fibers in the amount of about 2 to 2.5% by
volume are used. The fibers are cut from very fine, 360 ksi (2500 MPa) wire. Other
mixtures have been developed; for example, Tadros et al.
4
report on a mixture that uses
local aggregates and has a cost that is about 10% of the cost of early UHPC mixtures.
However, this mixture does not strictly meet the definition of UHPC because the
compressive strength is only 18 ksi (124 MPa).
Factors Inhibiting Widespread Use of UHPC
The original prebagged UHPC product introduced to the U.S. market had tight tolerance
specifications. The steel fibers had to be imported from abroad, which required a waiver
of Buy America requirements for many projects. As a result, the unit cost was relatively
high. In addition, the UHPC was expected to be mixed in high-energy mixers for 8 to
17 minutes, plus another 10 min. for loading the mixer and unloading the mixture into
a ready-mix truck or other transportation devices. However, Graybeal
3
has reported
that mixing of UHPC can be performed using conventional mixers, as long as high
energy input is provided. Temperature of the mixture, due to increased mixing time,
can be controlled through use of ice water. The steel fibers are now available from a
manufacturer in the United States.
Upon placement, the early development of UHPC called for curing for at least 48 hours
at a high, 90°C (194°F), temperature. Some of the original mixtures were also required
to be cured in high-pressure chambers. This is inconsistent with standard practice of
12- to 16-hour, overnight curing with maximum temperatures of 70°C (158°F). Loss of
productivity and high materials costs could result in a premium of 400% or more of the
cost of conventional concrete. This sharp increase cannot be offset by the anticipated
reduction in total quantities. Wille et al.
5
have demonstrated that an optimized mixture
can achieve the required strength without the originally required heat or pressure curing.
An effort is urgently needed in the United States to publish American Association
of Highway and Transportation Officials (AASHTO) specifications for design and
construction with UHPC. Australia, France, Japan and most recently Switzerland have
already published design recommendations and model code language.
The Malaysian Experience
Introduction of UHPC in Malaysia was started by a couple of engineers in 2006. The
company DURA was co-founded by Dr. Yen Lei Voo after he completed his Ph.D. in
Australia on the topic of UHPC. His advisor was Professor Stephen Foster, who had
been championing UHPC in Australia. Interestingly, the use of UHPC in Australia has
stagnated since the construction of its first bridge, the Shepherd Gully Creek Bridge,
Ultra-high-performance concrete (UHPC)
was first introduced as reactive powder
concrete in the early 1990s by the French
contractor Bouygues.
1
When introduced,
it came in two classes, Class 200 MPa
(29 ksi) and 800 MPa (116 ksi). Since
then, much research has been performed
by the Federal Highway Administration
(FHWA)
2
and researchers in other
countries around the world, including
Australia, Austria, Canada, Croatia,
France, Germany, Italy, Japan, Malaysia,
the Netherlands, New Zealand, Slovenia,
South Korea, Spain, Switzerland, and
the United Kingdom. In the United
States, several state depar tments of
transportation have expressed interest
in using UHPC in their bridge projects,
supported by FHWA research as well
as that done by their local universities.
Most notably, Virginia has produced
I-beams with UHPC and Iowa has built
two bridges with UHPC beams and one
with a UHPC deck. A significant interest
has recently been directed at using UHPC
in longitudinal joints between precast
concrete beams.
I t a p p e a r s t h a t t h e hig h c o s t o f
UHPC has discouraged owners from
implementing use of this outstanding
material in applications beyond the
initial demonstration projects, most of
which had been subsidized by government
technology implementation programs.
The exception to this trend has been the
significant success of the company DURA
Technology (DURA) in Malaysia. Over
70 bridges have been built by DURA in
that country since 2010. This article
provides a summary of the steps taken by
DURA to develop solutions with UHPC
that are cost-effective on a first-cost
basis. When the superior durability of
UHPC is factored in, its value increases
dramatically.
What is UHPC?
There is no universal definition of UHPC
or even its name. It appears that a
Taking Ultra-High-Performance Concrete to New Heights
The Malaysian Experience
by Dr. Maher K. Tadros, e.construct.USA LLC and Dr. Yen Lei Voo, DURA Technology